Who Is Responsible for Adware?

Updated April 12, 2006 12:01 a.m. ET

As adware continues to annoy computer users, efforts to crack down on ad-serving software have begun to focus on the advertisers behind some of the pop-ups.

New York Attorney General Eliot Spitzer, whose office has sued two major adware vendors, has threatened to come after advertisers. An affidavit filed last week with Mr. Spitzer's lawsuit against Internet marketer Direct Revenue named some large companies that continue to advertise through adware. (Direct Revenue, for its part, has said the case is "baseless"...